This invention relates to thermal-radiation detectors comprising a polymer film having a temperature-dependent characteristic to provide one or more infrared detector elements. The detector may comprise, for example, a linear array or 2-dimensional array of detector elements having pyroelectric and/or ferroelectric properties and may be used in, for example, an inexpensive infrared camera or other infrared imaging equipment.
Published European patent application EP-A-0 269 161 describes an example of a thermal-radiation detector comprising an infrared detector element or a group of infrared detector elements having first and second electrodes at respective first and second opposite faces of a flexible continuous film of polymer material having a temperature-dependent characteristic (pyroelectric in this case); the polymer material also has piezoelectric properties; and the polymer film is secured to a mounting arrangement to maintain the film taut. In the type of detector structure described in EP-A-0 269 161, the polymer film of, for example, a vinylidene fluoride copolymer is a quarter-wavelength thick to optimise radiation absorption with suitably resistive electrodes. The film is taut but not stretched, and the mounting arrangement comprises an electrically insulative annulus mounted on the header of the detector envelope. The periphery of the polymer film is bonded to the annulus so that the area of the detector element(s) is supported spaced from the header; hence this area of the second face of the film is free of contact with the mounting arrangement. This mounting arrangement reduces thermal conduction to and from the detector element(s). The whole contents of EP-A-0 269 161 are hereby incorporated herein as reference material.
In general, pyroelectric and ferroelectric materials are also piezoelectric. Hence the detector elements also produce electrical output if subjected to varying stress (for example by vibration and/or shock). This phenomenon, termed microphony, constitutes undesired background noise which interferes with the detection of the thermal radiation. This microphonic background noise forms part of the signal output from the detector elements to an electronic read-out circuit, and separation of this background noise from the infrared-generated signal component cannot be readily achieved in the read-out circuit.